--- a/dom/base/domerr.msg
+++ b/dom/base/domerr.msg
@@ -154,17 +154,18 @@ DOM4_MSG_DEF(NotSupportedError, "The med
 
 DOM4_MSG_DEF(SyntaxError, "The URI is malformed.", NS_ERROR_DOM_MALFORMED_URI)
 DOM4_MSG_DEF(SyntaxError, "Invalid header name.", NS_ERROR_DOM_INVALID_HEADER_NAME)
 
 /* XMLHttpRequest errors. */
 DOM4_MSG_DEF(InvalidStateError, "XMLHttpRequest has an invalid context.", NS_ERROR_DOM_INVALID_STATE_XHR_HAS_INVALID_CONTEXT)
 DOM4_MSG_DEF(InvalidStateError, "XMLHttpRequest state must be OPENED.", NS_ERROR_DOM_INVALID_STATE_XHR_MUST_BE_OPENED)
 DOM4_MSG_DEF(InvalidStateError, "XMLHttpRequest must not be sending.", NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_SENDING)
-DOM4_MSG_DEF(InvalidStateError, "XMLHttpRequest state must not be LOADING or DONE.", NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE)
+DOM4_MSG_DEF(InvalidStateError, "Cannot set 'responseType' property on XMLHttpRequest after 'send()' (when its state is LOADING or DONE).", NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_RESPONSE_TYPE)
+DOM4_MSG_DEF(InvalidStateError, "Cannot call 'overrideMimeType()' on XMLHttpRequest after 'send()' (when its state is LOADING or DONE).", NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_OVERRIDE_MIME_TYPE)
 DOM4_MSG_DEF(InvalidStateError, "responseXML is only available if responseType is '' or 'document'.", NS_ERROR_DOM_INVALID_STATE_XHR_HAS_WRONG_RESPONSETYPE_FOR_RESPONSEXML)
 DOM4_MSG_DEF(InvalidStateError, "responseText is only available if responseType is '' or 'text'.", NS_ERROR_DOM_INVALID_STATE_XHR_HAS_WRONG_RESPONSETYPE_FOR_RESPONSETEXT)
 DOM4_MSG_DEF(InvalidAccessError, "synchronous XMLHttpRequests do not support timeout and responseType.", NS_ERROR_DOM_INVALID_ACCESS_XHR_TIMEOUT_AND_RESPONSETYPE_UNSUPPORTED_FOR_SYNC)
 
 /* Image decode errors. */
 DOM4_MSG_DEF(EncodingError, "Node bound to inactive document.", NS_ERROR_DOM_IMAGE_INACTIVE_DOCUMENT)
 DOM4_MSG_DEF(EncodingError, "Invalid image request.", NS_ERROR_DOM_IMAGE_INVALID_REQUEST)
 DOM4_MSG_DEF(EncodingError, "Invalid encoded image data.", NS_ERROR_DOM_IMAGE_BROKEN)

--- a/dom/tests/mochitest/bugs/test_onerror_message.html
+++ b/dom/tests/mochitest/bugs/test_onerror_message.html
@@ -24,17 +24,17 @@ https://bugzilla.mozilla.org/show_bug.cg
 var expected = [
 { name: "Error", message: "foo", filename: String(location), lineNumber: 45 },
 { name: "Error", message: "foo", filename: "bar", lineNumber: 123 },
 { name: "", message: "uncaught exception: [object Object]" },
 { name: "DuckError", message: "foo", filename: "bar", lineNumber: 123 },
 { name: "", message: "uncaught exception: [object Object]" },
 { name: "", message: "foo", filename: "baz", lineNumber: 123 },
 { name: "", message: "uncaught exception: [object Object]" },
-{ name: "InvalidStateError", message: "XMLHttpRequest state must not be LOADING or DONE.", filename: String(location), lineNumber: 62 },
+{ name: "InvalidStateError", message: "Cannot set 'responseType' property on XMLHttpRequest after 'send()' (when its state is LOADING or DONE).", filename: String(location), lineNumber: 62 },
 { name: "ReferenceError", message: "xxx is not defined", filename: String(location), lineNumber: 64 },
 { name: "ReferenceError", message: "xxx is not defined", filename: String(location), lineNumber: 66 }
 ];
 
 var counter = 0;
 var origin = location.protocol + "//" + location.host;
 postMessage(counter, origin);
 window.onmessage = function(e) {

--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -627,17 +627,17 @@ nsresult XMLHttpRequestMainThread::Creat
 }
 
 void XMLHttpRequestMainThread::SetResponseType(
     XMLHttpRequestResponseType aResponseType, ErrorResult& aRv) {
   NOT_CALLABLE_IN_SYNC_SEND_RV
 
   if (mState == XMLHttpRequest_Binding::LOADING ||
       mState == XMLHttpRequest_Binding::DONE) {
-    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE);
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_RESPONSE_TYPE);
     return;
   }
 
   // sync request is not allowed setting responseType in window context
   if (HasOrHasHadOwner() && mState != XMLHttpRequest_Binding::UNSENT &&
       mFlagSynchronous) {
     LogMessage("ResponseTypeSyncXHRWarning", GetOwner());
     aRv.Throw(
@@ -3096,17 +3096,17 @@ void XMLHttpRequestMainThread::StartTime
 uint16_t XMLHttpRequestMainThread::ReadyState() const { return mState; }
 
 void XMLHttpRequestMainThread::OverrideMimeType(const nsAString& aMimeType,
                                                 ErrorResult& aRv) {
   NOT_CALLABLE_IN_SYNC_SEND_RV
 
   if (mState == XMLHttpRequest_Binding::LOADING ||
       mState == XMLHttpRequest_Binding::DONE) {
-    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE);
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_OVERRIDE_MIME_TYPE);
     return;
   }
 
   UniquePtr<MimeType> parsed = MimeType::Parse(aMimeType);
   if (parsed) {
     parsed->Serialize(mOverrideMimeType);
   } else {
     mOverrideMimeType.AssignLiteral(APPLICATION_OCTET_STREAM);

--- a/dom/xhr/XMLHttpRequestWorker.cpp
+++ b/dom/xhr/XMLHttpRequestWorker.cpp
@@ -2186,17 +2186,17 @@ void XMLHttpRequestWorker::SetResponseTy
     // Open() has not been called yet. We store the responseType and we will use
     // it later in Open().
     mResponseType = aResponseType;
     return;
   }
 
   if (mStateData.mReadyState == XMLHttpRequest_Binding::LOADING ||
       mStateData.mReadyState == XMLHttpRequest_Binding::DONE) {
-    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE);
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_RESPONSE_TYPE);
     return;
   }
 
   RefPtr<SetResponseTypeRunnable> runnable =
       new SetResponseTypeRunnable(mWorkerPrivate, mProxy, aResponseType);
   runnable->Dispatch(Canceling, aRv);
   if (aRv.Failed()) {
     return;

--- a/xpcom/base/ErrorList.py
+++ b/xpcom/base/ErrorList.py
@@ -634,17 +634,18 @@ with modules["DOM"]:
     errors["NS_ERROR_UNCATCHABLE_EXCEPTION"] = FAILURE(1015)
 
     errors["NS_ERROR_DOM_MALFORMED_URI"] = FAILURE(1016)
     errors["NS_ERROR_DOM_INVALID_HEADER_NAME"] = FAILURE(1017)
 
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_HAS_INVALID_CONTEXT"] = FAILURE(1018)
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_MUST_BE_OPENED"] = FAILURE(1019)
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_SENDING"] = FAILURE(1020)
-    errors["NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE"] = FAILURE(1021)
+    errors["NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_RESPONSE_TYPE"] = FAILURE(1021)  # NOQA: E501
+    errors["NS_ERROR_DOM_INVALID_STATE_XHR_MUST_NOT_BE_LOADING_OR_DONE_OVERRIDE_MIME_TYPE"] = FAILURE(1037)  # NOQA: E501
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_HAS_WRONG_RESPONSETYPE_FOR_RESPONSEXML"] = FAILURE(1022)
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_HAS_WRONG_RESPONSETYPE_FOR_RESPONSETEXT"] = FAILURE(1023)  # NOQA: E501
     errors["NS_ERROR_DOM_INVALID_STATE_XHR_CHUNKED_RESPONSETYPES_UNSUPPORTED_FOR_SYNC"] = FAILURE(1024)  # NOQA: E501
     errors["NS_ERROR_DOM_INVALID_ACCESS_XHR_TIMEOUT_AND_RESPONSETYPE_UNSUPPORTED_FOR_SYNC"] = FAILURE(1025)  # NOQA: E501
 
     # When manipulating the bytecode cache with the JS API, some transcoding
     # errors, such as a different bytecode format can cause failures of the
     # decoding process.